1. Field of the Invention
The present invention relates to a semiconductor device using an oxide semiconductor, a display device using the semiconductor device, and a manufacturing method thereof.
2. Description of the Related Art
In recent years, liquid crystal display devices typified by liquid crystal displays are becoming widespread. As a liquid crystal display, an active matrix liquid crystal display device provided with pixels each including a thin film transistor (TFT) is often used. In a thin film transistor included in an active matrix liquid crystal display device, amorphous silicon or polycrystalline silicon is used as an active layer. Although a thin film transistor using amorphous silicon has low field effect mobility, it can be easily formed over a large-sized substrate such as a large glass substrate. On the other hand, although a thin film transistor using polycrystalline silicon has high field effect mobility, it takes an enormous amount of time to form the thin film transistor using polycrystalline silicon over a large-sized substrate such as a large glass substrate because a crystallization process such as laser annealing is needed.
In view of the foregoing, techniques in which a thin film transistor is manufactured using an oxide semiconductor instead of the above silicon material and applied to electronic devices or optical devices have attracted attention. For example, Patent Document 1 and Patent Document 2 disclose a technique in which a thin film transistor is manufactured using zinc oxide or an In—Ga—Zn—O-based oxide semiconductor for an oxide semiconductor layer and such a transistor is used as a switching element or the like of an image display device.